A ceramic circuit board is used as a substrate on which a semiconductor element is mounted. Examples of the semiconductor elements may include various elements such as a power element, a light emitting diode (LED), a laser diode or the like. A conventional ceramic circuit board is formed by bonding a metal plate onto a ceramic substrate. Specifically, it has a structure in which materials are laminated in the order of metal-plate/ceramic-substrate/metal-plate. In such a laminated structure, there is a problem that a warp tends to occur in the ceramic circuit board due to the difference in thermal expansion coefficient between the ceramic substrate and the metal plate.
Semiconductor devices are increasing in output year by year, so as to exhibit a high power. Along with this increasing output power, the operation compensation temperature (i.e., junction temperature) is getting higher. It is said that the operation compensation temperature will be 150° C. for the seventh generation semiconductor and 175° C. or more for the eighth generation semiconductor. Thus, there has been also posed a problem such that the heat cycle resistance of the ceramic circuit board deteriorates due to the difference in thermal expansion coefficient between its constituent materials.
Further, in an adopted structure, a through-hole (via-hole) is provided in the ceramic substrate and the front and back (rear) of the ceramic circuit board are made to secure an electrical conduction with each other by this through-hole.
For instance, Japanese Unexamined Patent Application Publication No. 2006-287126 (Patent Document 1) discloses a structure for achieving the electrical conduction by a through hole. Patent Document 1 discloses a ceramic circuit board for mounting an LED.
In case of the through-hole type ceramic circuit board as disclosed in Patent Document 1, the metal plate is not bonded, and thus occurrence of a warp of the ceramic circuit board can be suppressed. On the other hand, in case of the ceramic circuit board disclosed in Patent Document 1, a portion on which the LED chip is mounted is formed to be convex, and thus polishing the ceramic substrate to form a convex shape is costly. Further, in the ceramic circuit board of Patent Document 1, a wiring pattern is provided on the surface of the through-hole, and thereafter the LED chip is mounted by soldering.